For displaying electronic images and information, two types of displays are predominant. The first is a cathode ray tube (CRT) and the other is a flat panel display. In a CRT display, such as is commonly used in television sets and computer monitors, red, green and blue light is generated and is mixed together to represent desired colors. In such a scheme, white balance can be carefully controlled by varying the intensity of each of the red, green, and blue light sources. Moreover, the overall intensity of the image can be controlled as well. Thus, CRT displays are capable of producing images with accurate color representation and good intensity. However, CRT displays tend to require a lot of space in order to allow for the tube along which the cathode projects the emissions that cause the phosphorescent glow on the front of the CRT display screen.
By contrast, flat panel displays require very little space. However, they generally suffer from being low intensity. One example of a flat panel display is a liquid crystal display (LCD). In high performance applications, the so-called AMLCD (active matrix liquid crystal display) is often employed.
In order to improve the visibility (brightness) of these flat panel displays, it has been known in the art to provide a backlight for directing light through the flat panel display to illuminate it from behind. The backlight is normally constructed of a light-combining wedge designed to be placed closely behind the flat panel display. The light-combining wedge is provided with light by multiple light sources (typically white light sources) positioned along the edges of the light-combining wedge. In order to ensure a proper white balance, the light sources (bulbs or lamps) are very carefully selected to have very specific output characteristics. This tends to require the use of very expensive lamps in order to ensure that the backlight provides reasonably good white balance. Unfortunately, not only must such lamps be high-performance and expensive, such arrangements tend to require very specific lamps, thereby making it impractical to use common or readily available lamps without adversely affecting the white balance of the display backlight. This also makes it difficult to achieve uniform performance in the manufacture of multiple copies of a backlight, as there can be slight performance variations from one lamp to the next. Also, such an arrangement can be difficult to adjust in the field in use to achieve the proper white balance.
Accordingly, it can be seen that a need yet remains for a backlight for a display, which backlight allows the use of standard, readily-available lamps, which allows a broad range of white balance compensation adjustment, and which can be adjusted in the field in use. It is to the provision of such a backlight that the present invention is primarily directed.